Found out so far, that mailmanager is broken:
same issue here. I installed 9.510 on my SG 105W at home. I´m not using mail protection, but I checked the mail manager before and after the installation.
After the installation i get the same error message "invalid request".
Maybe mail manager is no longer necessary... Sophos fixed the quarantine report release option for end users (NUTM-9836) instead ;)
Same error here! Luckily only on my test UTM